Generally, carrier tapes are used to store and transport compact electronic components such as IC's. In particular, polystyrene (PS) sheets are excellent in transparency and have good thermoforming properties, so they are widely used for being able to provide carrier tapes of good pocket shape (see, e.g., Patent Documents 1 and 2).
On the other hand, when transporting IC's, the buildup of static electricity due to friction between the carrier tape and the content, or generated when peeling cover tape adhered to the top surface of the carrier tape, can result in destruction of the IC circuits. Additionally, in the case of very small components, the components can adhere to the cover tape, causing problems when mounting them to electronic devices. In order to prevent such trouble, the surface of the carrier tape is often subjected to an anti-static treatment (see, e.g., Patent Documents 3 and 4). However, when treated with a normal anti-static agent, the surface resistance can become higher, and the anti-static effect can be insufficient. Therefore, methods of preventing the buildup of static electricity by providing a conductive layer comprising a conductive material such as carbon black or a metallic powder are known (e.g., Patent Document 5), but in that case, it is difficult to obtain sufficient transparency to read letters inscribed on the compact electronic components that are contained inside through the tape or to inspect the products as to whether or not they are acceptable.
Additionally, as anti-static treatments and conductivity treatments for the surface of films in general, processes of coating the surface of a substrate film consisting of polycarbonate (PC), polyethylene terephthalate (PET), polypropylene (PP) or the like and forming a conductive layer having a certain degree of transparency have been proposed for various applications (see, e.g., Patent Documents 6 to 8).
However, sheets and films coated with various types of conductive agents and conductive compositions on their surfaces as disclosed in Patent Documents 6 to 8 are such that the materials of the substrate films are mainly composed of PC, PET and PP substrates, and no specific examples have been disclosed in the technical field of the present invention of a favorable arrangement wherein the surface of a PS sheet is coated. Additionally, when forming pockets in carrier tape using a sheet having the surface of the substrate sheet of the material coated with a conductive agent, the surface resistance of the conductive layer can rise, reducing the effect of preventing the buildup of electrostatic charge. Furthermore, when a raw sheet is stored in a wound state, particularly in a high-temperature high-humidity environment, blocking and separation of the conductive layer due to blocking may occur.
Furthermore, Patent Document 9 discloses a laminated sheet comprising a conductive coating layer containing a polythiophene type polymer formed on the substrate sheet. However, the degree of contact between the conductive coating layer and the substrate sheet is still inadequate in this laminated sheet, and there is a risk of the conductive film layer separating from the substrate sheet.
Patent Document 1: JP 2003-55526 A
Patent Document 2: JP 2005-23268 A
Patent Document 3: JP 2003-253069 A
Patent Document 4: JP 2003-320605 A
Patent Document 5: JP H9-76424 A
Patent Document 6: IP 2003-308733 A
Patent Document 7: JP 2005-511808 T
Patent Document 8: JP 2007-157440 A
Patent Document 9: JP 2006-27266 A